Tri stable actuator apparatus and method

ABSTRACT

An actuator to direct a downhole drilling tool includes a stator and an armature configured to be electromagnetically displaced into one of three stable positions. A cavity within the stator is in communication with a high-pressure fluid and hydraulic ports in the stator allow the high-pressure fluid to communicate with low-pressure regions. Plungers on the armature selectively block either or none of the hydraulic ports, allowing for three control options from the actuator to the downhole drilling tool.

BACKGROUND OF THE INVENTION

The present invention generally relates to apparatuses and methods to actuate downhole drilling tools. More particularly, the present invention relates to downhole actuators to position a drill bit assembly in a desired trajectory by a rotary steerable assembly. More particularly still, the present invention relates to a tri-stable actuator to be used in a rotary steerable system to accommodate more precise positioning of a drill bit assembly.

Boreholes are frequently drilled into the Earth's formation to recover deposits of hydrocarbons and other desirable materials trapped beneath the Earth's crust. Traditionally, a well is drilled using a drill bit attached to the lower end of what is known in the art as a drillstring. The drillstring is a long string of sections of drill pipe that are connected together end-to-end through rotary threaded pipe connections. The drillstring is rotated by a drilling rig at the surface thereby rotating the attached drill bit. The weight of the drillstring typically provides all the force necessary to drive the drill bit deeper, but weight may be added (or taken up) at the surface, if necessary. Drilling fluid, or mud, is typically pumped down through the bore of the drillstring and exits through ports at the drill bit. The drilling fluid acts both lubricate and cool the drill bit as well as to carry cuttings back to the surface. Typically, drilling mud is pumped from the surface to the drill bit through the bore of the drillstring, and is allowed to return with the cuttings through the annulus formed between the drillstring and the drilled borehole wall. At the surface, the drilling fluid is filtered to remove the cuttings and is often used recycled.

In typical drilling operations, a drilling rig and rotary table are used to rotate a drillstring to drill a borehole through the subterranean formations that may contain oil and gas deposits. At downhole end of the drillstring is a collection of drilling tools and measurement devices commonly known as a Bottom Hole Assembly (BHA). Typically, the BHA includes the drill bit, any directional or formation measurement tools, deviated drilling mechanisms, mud motors, and weight collars that are used in the drilling operation. A measurement while drilling (MWD) or logging while drilling (LWD) collar is often positioned just above the drill bit to take measurements relating to the properties of the formation as borehole is being drilled. Measurements recorded from MWD and LWD systems may be transmitted to the surface in real-time using a variety of methods known to those skilled in the art. Once received, these measurements will enable those at the surface to make decisions concerning the drilling operation. For the purposes of this application, the term MWD is used to refer either to an MWD (sometimes called a directional) system or an LWD (sometimes called a formation evaluation) system. Those having ordinary skill in the art will realize that there are differences between these two types of systems, but the differences are not germane to the embodiments of the invention.

A popular form of drilling is called “directional drilling.” Directional drilling is the intentional deviation of the wellbore from the path it would naturally take. In other words, directional drilling is the steering of the drill string so that it travels in a desired direction. Directional drilling is advantageous offshore because it enables several wells to be drilled from a single platform. Directional drilling also enables horizontal drilling through a reservoir. Horizontal drilling enables a longer length of the wellbore to traverse the reservoir, which increases the production rate from the well. A directional drilling system may also be beneficial in situations where a vertical wellbore is desired. Often the drill bit will veer off of a planned drilling trajectory because of the unpredictable nature of the formations being penetrated on the varying forces that the drill bit experiences. When such a deviation occurs, a directional drilling system may be used to put the drill bit back on course.

A traditional method of directional drilling uses a bottom hole assembly that includes a bent housing and a mud motor. The bent housing includes an upper section and a lower section that are formed on the same section of drill pipe, but are separated by a permanent bend in the pipe. Instead of rotating the drillstring from the surface, the drill bit in a bent housing drilling apparatus is pointed in the desired drilling direction, and the drill bit is rotated by a mud motor located in the BHA. A mud motor converts some of the energy of the mud flowing down through the drill pipe into a rotational motion that drives the drill bit. Thus, by maintaining the bent housing at the same azimuth relative to the borehole, the drill bit will drill in a desired direction. When straight drilling is desired, the entire drill string, including the bent housing, is rotated from the surface. The drill bit angulates with the bent housing and drills a slightly overbore, but straight, borehole.

A more modern approach to directional drilling involves the use of a rotary steerable system (RSS). In an RSS, the drill string is rotated from the surface and downhole devices force the drill bit to drill in the desired direction. Rotating the drill string is preferable because it greatly reduces the potential for getting the drillstring stuck in the borehole. Generally, there are two types of RSS, “point the bit” systems and “push the bit” systems. In a point system, the drill bit is pointed in the desired position of the borehole deviation in a similar manner to that of a bent housing system. In a push system, devices on the BHA push the drill bit laterally in the direction of the desired borehole deviation by pressing on the borehole wall.

A point the bit system works in a similar manner to a bent housing because a point system typically includes a mechanism to provide a drill bit alignment that is different from the drill string axis. The primary differences are that a bent housing has a permanent bend at a fixed angle and a point the bit RSS typically has an adjustable bend angle that is controlled independent of the rotation from the surface. A point RSS typically has a drill collar and a drill bit shaft. The drill collar typically includes an internal orienting and control mechanism that counter rotates relative to the rotation of the drillstring. This internal mechanism controls the angular orientation of the drill bit shaft relative to the borehole. The angle between the drill bit shaft and the drill collar may be selectively controlled, but a typical angle is less than 2 degrees. The counter rotating mechanism rotates in the opposite direction of the drill string rotation. Typically, the counter rotation occurs at the same speed as the drill string rotation so that the counter-rotating section maintains the same angular position relative to the inside of the borehole. Because the counter rotating section does not rotate with respect to the borehole, it is often called “geo-stationary” by those skilled in the art.

Most rotary steerable systems involve the conversion of energy in the drilling fluids into mechanical energy. Drilling fluids are typically delivered to the drill bit through a bore of the drillstring and return through the annulus formed between the borehole and the outer diameter of the drillstring. Therefore, because the cross-sectional area of the bore of the drillstring is smaller than the cross-sectional area of the annulus, the drillstring bore fluid pressures are significantly higher than those in the annulus. This pressure differential is of great importance to drilling operations as it allows various devices to use the pressure differential to generate work and power downhole. The rotary steerable system is such a device, often employing the pressure differential between delivered and returning drilling fluids to activate thrust pads and bend angle actuators to achieve the rotary steerable effect of the downhole drilling apparatus.

Former downhole actuators used with rotary steerable systems acted to divert the high-pressure drilling fluids from the bore of the drillstring to various devices to produce mechanical work and push against the drilled formation in various directions. These actuators were typically electromagnetically activated and are constructed as bi-stable actuators having only “on” and “off” positions. Typically, to maintain a bi-stable electromagnetic actuator into one of its positions, powerful permanent magnets were used to retain an armature in the designated position. To overcome the retaining force of the permanent magnets, higher currents were necessary to break the armature free of the permanent magnets that would have otherwise been necessary to displace the armature. As such, former bi-stable actuators consumed more energy in switching positions than necessary. An actuator requiring less energy to switch between two or more stable positions would be highly desirable in the oilfield today.

SUMMARY OF THE INVENTION

The deficiencies of the prior art are addressed by an actuator to direct a rotary steerable tool. The actuator preferably includes a stator having an internal cavity in communication with a high-pressure zone, a first hydraulic port and a second hydraulic port. The actuator preferably includes an armature housed within the internal cavity, wherein the armature includes a first valve plunger and a second valve plunger. Preferably, the first valve plunger is configured to block the first hydraulic port from the high-pressure zone when the armature is in a first position and the second valve plunger is configured to block the second hydraulic port from the high-pressure zone when the armature is in a second position. Preferably, the first and second hydraulic ports are in communication with the high-pressure zone when the armature is in a third position and the actuator is configured to be electromagnetically displaced into the first and second positions.

The deficiencies of the prior art are also addressed by a method to operate a rotary steerable tool with a tri-stable actuator. The method preferable includes installing an armature within an internal cavity of a stator, wherein the stator has a first hydraulic port and a second hydraulic port. The method preferably includes hydraulically communicating between a high-pressure zone and the internal cavity. The method preferably includes blocking the first hydraulic port and communicating between the high-pressure zone and the second hydraulic port when the stator is in a first position. The method preferably includes blocking the second hydraulic port and communicating between the high-pressure zone and the first hydraulic port when the stator is in a first position. The method preferably includes communicating between the high-pressure zone and both first and second hydraulic ports when the stator is in a third position. The method preferably includes displacing the stator into the first and the second positions with electromagnetic force.

The deficiencies of the prior art are also addressed by a tri-stable actuator. The tri-stable actuator preferably includes a stator having an internal cavity in communication with a high-pressure zone, a first hydraulic port and a second hydraulic port. The tri-stable actuator preferably includes an armature housed within the internal cavity, wherein the armature includes a first valve plunger and a second valve plunger. Preferably, the first valve plunger is configured to block the first hydraulic port from the high-pressure zone when the armature is in a first stable position. Preferably, the second valve plunger is configured to block the second hydraulic port from the high-pressure zone when the armature is in a second stable position. Preferably, the first and second hydraulic ports are in communication with the high-pressure zone when the armature is in a third stable position and the actuator is configured to be electromagnetically displaced into the first and second stable positions. Preferably, the armature is configured to be held into the first stable position by the force of fluids flowing from the high-pressure zone through the second port and held into the second stable position by the force of fluids flowing from the high-pressure zone through the first port.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a tri-stable actuator in accordance with an embodiment of the present invention.

FIG. 2 is a schematic representation of the tri-stable actuator of FIG. 1 engaged in a first position.

FIG. 3 is a schematic representation of the tri-stable actuator of FIG. 1 engaged in a second position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring initially to FIG. 1, a tri-stable actuator assembly 100 in accordance with an embodiment of the present invention is shown schematically. Tri-stable actuator assembly 100 is shown having a stator 102 and an armature 104. Stator 102 preferably is in communication with high-pressure fluids and has two ports 106, 108 in communication with lower pressure zones. Actuator 100 selectively diverts high-pressure flow (e.g. drilling fluids) from internal cavity 110 to low-pressure ports 106, 108. Biasing springs 112, 114 between stator 102 and armature 104 centralize armature 104 along its axis 116 within stator 102 when no other forces are present. Armature 102 is shown in FIG. 1 in a neutral position, one where both port 106 and 108 are unobstructed and in communication with high-pressure fluids inside cavity 110. Because ports 106 and 108 are of substantially the same size and geometry and because armature 104 is symmetrical, high-pressure fluid flowing from cavity 110 through ports 106,108 will not displace armature 104 with respect to stator 102 along axis 116. As such, with armature 102 in position shown in FIG. 1, high-pressure fluid flows through both ports 106 and 108 at substantially the same rate to drive any equipment attached thereto with equal amounts of energy.

Furthermore, stator 102 and armature 104 are preferably components of an electromagnetic system whereby armature is thrust along its axis 116 to close ports 106 and 108. Typically, an electromagnetic system comprises a magnetic field and an electric coil. The field is preferably a permanent magnet but can be constructed as an electromagnet, one that requires electric current to be magnetized, if desired. The electric coil is preferably constructed as a coil of electrically conductive wire. The number of coils, the gauge of the wire, and the amount and potential of current applied thereto designate the amount of electromagnetic force. Depending on the polarity of the electrical charge applied to the coil, the coil will create a magnetic force that interacts with the magnetic properties of the field. If the poles of the field and the coil are reversed, they are attracted to one another. If the poles are aligned, then they are repelled.

In FIG. 1, stator 102 is shown constructed as field and armature 104 is constructed as a coil. While this configuration is preferred, it should be understood that alternate configurations could be accomplished by one of ordinary skill without departing from the spirit of the present invention. When constructed as a coil, Armature 104 is able to conserve mass. The operation of armature 104 is more efficient and exhibits greater responsiveness when the mass thereof is minimized. Stator 102 is shown constructed from a ferromagnetic material having a positive pole (+) and a negative pole (−). Alternatively, stator 102 can be constructed as an electromagnetic device also having a coil so that the magnitude and polarity of the magnetic field generated thereby can be varied or reversed. With no current applied to coil of armature 104, springs 112 and 114 center armature upon axis 116 and allow hydraulic communication between both ports 106 and 108 and high-pressure fluids within cavity 110. When either port 106 or 108 is intended to be closed, an electrical current is applied to the coil of armature 104 and one of two plungers 118, 120 is driven into port 106 and 108, depending on the polarity of armature 104 with respect to the polarity of stator 102.

If the forces from springs 112, 114 are not strong enough to maintain armature 104 in a centralized position between ports 106 and 108, an electromagnetic device 122 of stator 102 can be used in conjunction with a corresponding electromagnetic device 124 of armature 104 to retain armature 104. Using electromagnetic devices 122, 124, armature 104 can be kept clear of ports 106, 108 in circumstances where high turbulent flow from high-pressure cavity 110 through ports 106, 108 might otherwise cause movement of armature 104 along axis 116. Furthermore, since it can be difficult to extend electrical leads to armature 104 from inside cavity 110 of stator 102, springs 112, 114 can optionally be constructed as electrical conductors to activate coils within armature 104. Alternatively, armature 104 can be constructed as a permanent magnetic field and stator 102 can contain the electrical coil.

Referring briefly now to FIG. 2, actuator assembly 100 is shown with armature 102 displaced such that plunger 118 is in engaged within port 106 allowing high-pressure fluids to flow from cavity 110 only through port 108. The particularities of the seal between plunger 118 and port 106 (or plunger 120 and port 108) are not shown, but as long as engagement of plunger 118 into or against port 106 acts to seal off port 106 with sufficient integrity, the actuator assembly 100 functions as desired. Therefore, port 106 can include a socket configured to seal with plunger 118 or the face of plunger 118 can alternatively be configured to seal access to port 106 without engagement therein.

Furthermore, once plunger 118 of actuator assembly 100 engages port 106, electromagnetic force is no longer required to retain armature 104 in its displaced position so long as pressure of fluids flowing from cavity 110 through port 108 is maintained. High-pressure fluids flowing from cavity 110 through port 108 act upon face 126 and thrust plunger 118 further into engagement with port 106. As such, considerable electrical energy is conserved in that actuator assembly 100 is considered “stable” in the position shown in FIG. 2. To disengage plunger 118 from port 106, only enough current is needed to activate to coil within armature 104 to overcome the pressure forces thrusting against face 126. Former systems either required continuous current to flow through coil of armature 104 or permanent magnets to retain a plunger within a port. The former systems necessitated that current to be consumed throughout the engagement period and the latter system required elevated current to disengage the armature from the permanent magnet holding the plunger in place. The actuator assembly 100 of the present invention only consumes electrical energy when the position of armature 104 is changed and requires less current than prior art systems in changing that position.

Referring briefly to FIG. 3, actuator assembly 100 is shown with armature 104 displaced such that plunger 120 is engaged with port 108. Like the position of armature 104 in FIG. 2, the position of armature 104 shown in FIG. 3 is also “stable” when no current flows through armature 104 or stator 102 as high-pressure fluids flowing from cavity 110 through port 106 act upon face 128 to keep plunger 120 engaged. Similarly, as there is no magnetic force holding plunger 120 in engagement with port 108, electrical current in coil of armature 102 is only required to overcome the force of the flow against face 128.

Actuator assembly 100 has three “stable” positions, shown in FIGS. 1, 2, and 3 respectively, enabling various modes of communication between high-pressure fluids in cavity 110 and ports 106 an 108. Particularly, Actuator 100 has three selectable modes: 1) port 106 in communication with cavity 110; 2) port 108 in communication with cavity 110; and 3) both ports 106 and 108 in simultaneous communication with cavity 110. With these three modes, a rotary steerable system (or any other downhole tool) using tri-stable actuator 100 in accordance with the present invention can divert drilling fluids in one of three ways to enable the tool to be more precisely controlled and much more efficiently.

Former systems consumed more electrical energy than the tri-stable actuator 100 of the present invention and only provided for two positions, on and off. Therefore, former systems required the installation and control of several actuators to completely control a downhole tool. Using actuators in accordance with the present invention, the tool designer has the option of either using fewer actuators (thereby conserving valuable space) or using the same number of actuators, but with much more precise control than previously possible. Most downhole systems operate on limited power supplies that are either generated downhole or delivered and stored downhole in lithium battery packs. Because the power output of these devices is always finite, a reduction in electrical power consumption of downhole equipment is highly desirable.

Numerous embodiments and alternatives thereof have been disclosed. While the above disclosure includes the best mode belief in carrying out the invention as contemplated by the inventors, not all possible alternatives have been disclosed. For that reason, the scope and limitation of the present invention is not to be restricted to the above disclosure, but is instead to be defined and construed by the appended claims. 

1. An actuator to direct a rotary steerable tool, the actuator comprising: a stator having an internal cavity in communication with a high-pressure zone, a first hydraulic port and a second hydraulic port; an armature housed within said internal cavity, said armature including a first valve plunger and a second valve plunger; said first valve plunger configured to block said first hydraulic port from said high-pressure zone when said armature is in a first position; said second valve plunger configured to block said second hydraulic port from said high-pressure zone when said armature is in a second position; said first and said second hydraulic ports in communication with said high-pressure zone when said armature is in a third position; and said actuator configured to be electromagnetically displaced into said first and said second positions.
 2. The actuator of claim 1 wherein said armature includes an electromagnetic coil to generate electromagnetic force when energized by a power source.
 3. The actuator of claim 1 wherein said stator comprises a ferromagnetic material.
 4. The actuator of claim 1 wherein said stator comprises an electromagnetic coil to generate electromagnetic force when energized by a power source.
 5. The actuator of claim 1 wherein said armature comprises a ferromagnetic material.
 6. The actuator of claim 1 further comprising a first spring to bias said first valve plunger away from said first hydraulic port and a second spring to bias said second valve plunger away from said second hydraulic port.
 7. The actuator of claim 6 wherein said first and said second springs act as electrical leads in communication with an electromagnetic coil of said armature.
 8. The actuator of claim 1 wherein said armature is held into said first position by the force of fluids flowing from said high-pressure zone through said second port.
 9. The actuator of claim 1 wherein said armature is held into said second position by the force of fluids flowing from said high-pressure zone through said first port.
 10. The actuator of claim 1 wherein said armature is held into said third position through electromagnetic force.
 11. The actuator of claim 1 wherein said armature is held into said third position by the force of fluids flowing from said high-pressure zone simultaneously through said first and said second ports.
 12. A method to operate a rotary steerable tool with a tri-stable actuator, the method comprising: installing an armature within an internal cavity of a stator, the stator having a first hydraulic port and a second hydraulic port; hydraulically communicating between a high-pressure zone and the internal cavity; blocking the first hydraulic port and communicating between the high-pressure zone and the second hydraulic port when the stator is in a first position; blocking the second hydraulic port and communicating between the high-pressure zone and the first hydraulic port when the stator is in a first position; communicating between the high-pressure zone and both first and second hydraulic ports when the stator is in a third position; and displacing the stator into the first and the second positions with electromagnetic force.
 13. The method of claim 12 further comprising biasing the armature away from the first position with a first spring.
 14. The method of claim 12 further comprising biasing the armature away from the second position with a second spring.
 15. The method of claim 12 further comprising retaining the armature in the first position with the force of fluid flowing from the high-pressure zone through the second hydraulic port.
 16. The method of claim 12 further comprising retaining the armature in the second position with the force of fluid flowing from the high-pressure zone through the third hydraulic port.
 17. The method of claim 12 further comprising retaining the armature in the third position with electromagnetic force.
 18. A tri-stable actuator comprising: a stator having an internal cavity in communication with a high-pressure zone, a first hydraulic port and a second hydraulic port; an armature housed within said internal cavity, said armature including a first valve plunger and a second valve plunger; said first valve plunger configured to block said first hydraulic port from said high-pressure zone when said armature is in a first stable position; said second valve plunger configured to block said second hydraulic port from said high-pressure zone when said armature is in a second stable position; said first and second hydraulic ports in communication with said high-pressure zone when said armature is in a third stable position; said actuator configured to be electromagnetically displaced into said first and said second stable positions; and said armature is configured to be held into said first stable position by a force of fluids flowing from said high-pressure zone through said second port and held into said second stable position by said force of fluids flowing from said high-pressure zone through said first port.
 19. The tri-stable actuator of claim 18 further comprising a first spring to bias said first valve plunger away from said first hydraulic port and a second spring to bias said second valve plunger away from said second hydraulic port. 